542 SUPPLEMENT 
there may, however, be remarked on it, some pairs of sub- 
circular scales, a little concave, and which are exactly placed 
two by two, in the direction of the ray, which should go into 
the interstice of the teeth; each is pierced with an orifice. 
Around the anus the coronal pieces fill almost com- 
pletely the spaces which are left by the areas. They are, like 
these latter, ten in number, alternately great and small. All 
of them are usually granular, and pierced with a hole, much 
broader, however, in the Jarge than in the small ones, which 
correspond to the ambulacraria ; the large ones correspond to 
the anambulacraria. 
The holes with which the pieces of the ambulacraria are 
pierced, give passage to small tentacular cuppers, proceeding 
from the interior lamina of the skin, perhaps, from the hollow 
respiratory lamine in their entire length, and terminated at 
their extremity by a small swelling susceptible of being di- 
lated into a cupper, or into a disk denticulated at its circum- 
ference. 'These organs are remarkable for the great contrac- 
tility which they possess, and can re-enter completely into the 
interior, something like the horns of snails, or be considerably 
elongated at the exterior. 
Another portion of the locomotive apparatus of the echini, 
is that from which their name is taken, though more frequently 
these organs merit the name of little clubs, or tubercles, ra- 
ther than that of bristles. What they offer in common, is the 
having at their base, a small spherical concave head, with a 
circular pad above. Their length, their form, and their thick- 
ness, are extremely variable, and generally in relation with 
those of the mammille of the testa. Their structure is equally 
peculiar. When broken they have a vitreous sort of brilli- 
ancy. ‘Their external surface is almost always finely striated, 
and they are composed of concentric strata, each of which is 
formed of a great number of irradiated fibres. 
These organs, articulated like a knee on the mammille of 
